MICROSTRUCTURAL MODELING OF AUXETIC MICROPOROUS POLYMERS

A simple two-dimensional model for the deformation of auxetic micropor ous polymers (those with a negative Poisson's ratio) has been develope d. This model network of rectangular nodules interconnected by fibrils has been further developed to include the possibilities of fibril hin ging, flexure and stretching. Expressions for strain-dependent Poisson 's ratio and Young's modulus have been derived and compared with exper imental results on microporous PTFE and UHMWPE. A combination of the h inging mode followed by the stretching mode of deformation can be used to explain the general features of the experimental data for these au xetic polymers. The force coefficients governing the different modes o f deformation are dependent on fibril dimensions and intrinsic materia l properties. By varying the geometry of the network, the model can be used to predict different combinations of Poisson's ratio with modulu s, from large positive through to large negative values.